1. Field of the Invention
The present invention relates to the use of wireless technology to estimate the position of a person or device. It particularly relates to a radio transceiver arranged to determine its location by receiving messages transmitted from a first plurality of proximal radio transceivers and also arranged to facilitate the determination of the location of a second proximal radio transceiver by transmitting a message or messages to that second proximal transceiver and to ad hoc networks formed by arrangements of such transceivers.
2. Description of the Prior Art
It is often desirable to be able to determine one's position or to determine the position of another person or device. The Global position system (GPS) allows the location of specialist receivers to be positioned on the surface of the earth. GPS uses a fixed network of satellite transmitters orbiting the earth to transmit to and thereby locate the receiver. Cellular positioning systems have also been proposed in which the existing network of fixed base station transceivers is used to locate a mobile phone. The unchanging position and identity of the fixed base stations and the distance of the mobile phone from the base stations is used to estimate the phones location. Both of these systems operate over large distances exceeding many kilometres.
A radio location system suitable for tracking objects over shorter distances is proposed in U.S. Pat. No. 5,119,104. A fixed array of receivers is distributed over the area and a transmitter is attached to the object to be tracked. Time of arrival measurements of transmitted signals at the distributed receivers are used to locate the object.